Brake pedal fade only when car is running

Having now sorted out the problem with the hand brake I now have another issue that I was hoping you guys might be able to help with.

The brake pedal pressure level seems constant when the engine is off but when I start the car and I apply the brakes the pedal hits the floor and I have no brakes. If I lift off though and reapply the brakes they seem to working again.

Anyone experienced this at all?

Hakydan wrote:Having now sorted out the problem with the hand brake I now have another issue that I was hoping you guys might be able to help with.

The brake pedal pressure level seems constant when the engine is off but when I start the car and I apply the brakes the pedal hits the floor and I have no brakes. If I lift off though and reapply the brakes they seem to working again.

Anyone experienced this at all?

I've had that with a dodgy master cylinder, though that didn't just apply when the engine was running. Only other possible culprit is the vacuum servo? If it only happens the once when you first start the car, it may even be a brake pad(s) sticking in the caliper(s)?

Did you sort this out?, I have a similar thing happening!

I've just replaced the rear pressure regulating valve and 1 caliper on the rear + new copper pipes on the rear.

I first thought it was air bubbles, but bleed it for ages on the rear left especially.

I had this once before, but i pumped the brake pedal and the master cylinder seemed to click then the brake pressure was nice and strong, this times its just staying soft but only when engines running?! anyone got any ideas i can try?


bloody annoying i've only got a few days left of the free retest.

I've also got some mk3 golf gti calipers coming this week that have the same fixing centers, be nice to try and get them on as the standard Uno rears are troublesome!